Preparation and NMR study of silylated carboxonium ions.

A series of silylated carboxonium ions, 2a-6a, were prepared as long-lived species by treating triethylsilane and triphenylmethyl tetrakis(pentafluorophenyl)borate (Ph3C(+)B(C6F5)4-) with ketones, enones, carbonates, amides, and urea in CD2Cl2 solution. They were characterized by 13C and 29Si NMR spectroscopy at -78 degrees C. The NMR study indicates that the silylated carbonyl compounds are resonance hybrids of oxocarbenium and carboxonium ions, while the latter are the major contributors to the overall structures. The structure and 13C and 29Si NMR chemical shifts of the model trimethylsilylated carboxonium ions were also calculated by density functional theory/IGLO methods. The calculated results agree well with the experimental data.

通过在二氯甲烷溶液中用三乙基硅烷和四（五氟苯基）硼酸三苯甲基（Ph₃C⁺B(C₆F₅)₄⁻）处理酮、烯酮、碳酸酯、酰胺和尿素，制备了一系列甲硅烷基化的羰基鎓离子2a - 6a作为长寿命物种。在 - 78℃下通过¹³C和²⁹Si核磁共振波谱对它们进行了表征。核磁共振研究表明，甲硅烷基化的羰基化合物是氧鎓离子和羰基鎓离子的共振杂化体，而后一种离子对整体结构起主要作用。还通过密度泛函理论/IGLO方法计算了模型三甲基甲硅烷基化羰基鎓离子的结构以及¹³C和²⁹Si核磁共振化学位移。计算结果与实验数据吻合良好。